1. Field of the Invention
The present invention relates to bioresorbable pin systems useful for the reduction of bone fragments and for fixing barrier membranes used in conjunction with guided bone regeneration procedures, particularly pins having a detachable handle and a pre-fabricated hole in the handle to facilitate its removal following detachment from the pin.
2. Description of the Related Art
A variety of bone and membrane fixation devices are known, including screws, pins, stables, cables and anchors. These devices are formed of a number of compositions, are available in a wide variety of shapes and have a variety of surface textures. See, e.g. U.S. Pat. No. 5,716,358 to Ochoa et al, "Directional Bone Fixation Device" (1998). However, metal implants are generally undesirable because they are associated with osteopenia and allergic reactions, and often require a second operation for their removal after the bone has healed. Accordingly, several resorbable products have been developed to provide anatomical reduction of bony fragments produced by a fracture.
A. Bioresorbable Pins
Various compositions have been used to form resorbable pins and screws, including polydioxanone and polyglycolide. These compositions tend to degrade and lose strength within days to weeks. Thus, their main use is for fast-healing fractures. Resorbable fixation devices for torn bodily material are described in U.S. Pat. No. 5,236,431 to Gogolewski et al., "Resorbable Fixation Device with Controlled Stiffness for Treating Bodily Material In Vivo and Introducer Therefore" (1993). Also known in the art are absorbable self-locking screw and plate systems for internal fixation of bone fractures and for tendon-to-bone attachment, as described, for example, in U.S. Pat. No. 5,275,601 to Gogolewski et al., "Self-locking Resorbable Screws and Plates for Internal Fixation of Bone Fractures and Tendon-to-bone Attachment" (1994).
Recently, a pin comprising 70:30 poly(L, DL-lactide), and known as the Polypin.RTM. was developed, and has improved degradation and strength characteristics appropriate for use in reducing slow-healing fractures. See, e.g., Claes et al., "New bioresorbable pin for the reduction of small bony fragments: design, mechanical properties and in vitro degradation," Biomaterials 17(16):1621-1626 (1996).
The Polypin.RTM. is an injection molded product of cylindrical shape, and having a length of 35 mm and a diameter of 2 mm. A small head, having a diameter of 2.6 mm allows the application of light compressive forces to the fragment to be fixed in place. Transverse ridges of 0.15 mm thickness provide a press fit of the pin into a pre-drilled bore hole in the bone. In use, as described by Claes et al., a drill hole of about 0.8 mm in diameter and about 2.6 mm in length in the head of the pin, is filled with an X-ray contrast marker to allow detection of the pin by X-ray.
B. Guided bone regeneration
Guided bone regeneration is a technique used to facilitate, for example, the use of dental implants in certain procedures where regeneration of bone or the incorporation of bone substitutes is desired. In the dental context, guided bone regeneration can be used successfully to promote bone formation in osseous deformities and defects in conjunction with teeth or endosseous implant placement. Osseous defects consist mainly of periodontal extraction sites, dehiscences or fenestrations, and localized ridge deformities. In addition, bone defects may either provide natural space making or be non-space making. Non-space making defects usually require bone graft materials to assist in space maintenance and to enhance bone formation. See, e.g., Mellonig, "Guided bone regeneration of bone defects associated with implants: an evidence-based outcome assessment." Int. J Periodontics Restorative Dent. 15 (2): 168-85 (1995); U.S. Pat. No. 5,839,899 to Robinson, "Method and Apparatus for Growing Jaw Bone Utilizing a Guided-tissue Regeneration Plate Support and Fixation System" (1998); and U.S. Pat. No. 5,511,565 to Syers, "Guided Bone and Tissue Generation Device and Method to Be Used During or After Dental Surgery or Jaw Surgery" (1996).
Fixation pins, as described above, are used in such guided bone regeneration procedures, with or without graft materials. For example, stainless steel bone pins have been used with decalcified freeze-dried bone allograft for localized ridge augmentation. Doblin, et al., "A Histologic Evaluation of Localized Ridge Augmentation Utilizing DFDBA in Combination with e-PTFE Membranes and Stainless Steel Bone Pins in Humans." Int. J Periodontics Restorative Dent., 16 (2): 120-9 (1996). Similarly, resorbable pins are used with various oral implants. See, e.g., Hurzeler et al., "Guided Bone Regeneration Around Exposed Implants: A New Bioresorbable Device and Bioresorbable Membrane Pins," Practical Periodontics and Aesthetic Dentistry 7(9):37-49 (1995). Moreover, pins also are used in cranial surgery where bone regeneration is involved. See, e.g., Eppley, "Potential for Guided Bone Regeneration and Bone Graft Fixation with Resorbable Membranes in Pediatric Craniofacial Surgery," J Craniofacial Surgery, 8(2):127-128 (1997).
In fact, one of the major uses for bioresorbable pins is to fix or stabilize barrier membranes that are themselves bioresorbable. See, Hurzeler et al., cited above. Such membranes are used to block the ingrowth of fibrous connective tissue, thereby encouraging bone cells to colonize the area adjacent to an implant. See, e.g., U.S. Pat. No. 5,609,881 to Ikada, "Biodegradable/Absorbable Barrier Membrane" (1997); and Piatelli, "Bone Formation inside the Material Interstices of e-PTFE Membranes: A Light Microscopical and Histochemical Study in Man," Biomaterials 17(17):1725-1731 (1996).
C. Pin Installation Systems
A variety of systems exist for installing pins used for various orthopedic and dental purposes. For example, the BioTack.TM. delivery system is useful for fixing bioabsorbable membranes. Pins come prepackaged in a sterile container with specifically designed friction fit drivers that are used to pick up and to deliver the pins to the site where bioabsorbable membranes are to be fixed for purposed of guided bone restoration.
Retentive dental pins also have been described, which comprise a lower portion that can be secured within the dentine of a tooth and an enlarged head portion to which a tooth restoration may be secured. For example, as shown in FIG. 1 of U.S. Pat. No. 5,263,996 to Filhol, "Dental Pin" (1993), a head portion (3) is connected, via a shearable connection (4) to a fixing portion (5) that is used to insert the pin into a tooth. Somewhat similar are the pins shown in FIGS. 1 and 2 of U.S. Pat. No. 4,171,569 to Rovins, "Dental Pin" (1979). In this system, a handle (4) includes fracture grooves (3) and (7) which are intended to break leaving the pin protruding from the tooth in order to anchor a superstructure on an excavated tooth.
What has been missing in the art, however, are appropriately-configured resorbable pins with handles to facilitate manual insertion of the pins, and associated techniques for using such pins, to facilitate the insertion of such pins for the fixation of bony fragments and barrier membranes, without the need for specialized tools, and that also facilitate removal of a severable handle portion after insertion of the pin portion into the bone.